( i ) continued The scale is
set to zero by screwing the control screw fully home in
a clockwise direction using a slightly tight feel (approx. 20 ozf in)
to prevent excessive end loading of the rotor. Slacken the scale,
set to zero indication, and lock in position. This operation is
carried out with the engine stationary and without fuel pressure.
The displaced volume of fuel through the metering unit can now be
calculated in terms of cubic millimeters per injection. For
an 8mm dia. shuttle the displacement is 1.28 cubic mm per 0.001 in of
shuttle stroke. For units supplied with a 6mm dia. shuttle the
displacement is 0.718 cubic mm per 0.001 in of shuttle stroke.
( ii
)
Metric measurement
For metric measurement of shuttle travel the micrometer spindle
is machined with a thread pitch of 0.5 mm and the control wheel divided
into 50 divisions. One division therefore equals 0.01 mm travel.
For an 8 mm dia. shuttle the displacement of fuel per 0.01 mm equals
0.503 cubic mm. For a 6 mm dia. shuttle the displacement of fuel
per
0.01 mm equals 0.283 cubic mm.
( iii
)
Full Load Setting - Maximum Fuel Stroke
The optimum fuel setting is obtained at all engine speeds at full
throttle. From the results, a compromise single fixed setting must
be chosen. This point ( 'A' on illustration LSK545) becomes the
maximum fuel setting on the final control cam.
( ii
)
Idle or No Load Setting - Minimum Fuel Stroke
With the engine set to idle at no load at the engine speed chosen,
the optimum fuel stroke is obtained. This point ( 'B' on the typical
curve) becomes the minimum fuel setting on the final control cam.
( v
)
Intermediate or Part Load settings
Engine throttle travel is subdivided into a scale representing
varying throttle openings, i.e. 3/4, 1/2, 1/4, 1/8 of full throttle. In the
case of a slide-type throttle this will be linear travel, for a butterfly
throttle it will be angular movement.
At each throttle setting the engine load is adjusted to allow the
engine to run at each of the chosen range of speeds. The optimum
fuel setting for each of these speeds is obtained, and from the
results a compromise fixed setting must be chosen, so providing an
intermediate point on the control curve.
The control curve can now be drawn in, passing through the
chosen points at
each throttle opening. This curve is now translated to the control cam
form, so
that the correct relationship of fuel stroke to throttle position is achieved.
Subsequent road test experience may call for small
adjustments to the cam form
to assist the throttle response.
The above work will often be carried out at the same time
as manifold
development, injector location and injection timing investigations.
Care
must be taken to ensure that the characteristics upon which the curve is based
refer to the finalized form of the above factors.
-4-
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